Currently, the electrical and electronic industry develops rapidly, and electronic products tend to be of lightweight, high performance, high reliability and environmental protection. Electronic circuit boards are also specifically required to be of high heat-resistance, low thermal expansion coefficient, high moisture resistance, environmental protection and flame retardant, low dielectric constant and dielectric loss, and high elastic modulus. Thus the conventional epoxy resin cannot completely meet the developing requirements on electronic circuit boards, and the applications of polyphenylene oxide resin having high heat-resistance, low dielectric constant and dielectric loss and excellent toughness in electronic circuit boards are more and more prominent. Due to high molecular weight, the conventional polyphenylene oxide resin is still deficient in processability.
Due to environmental pollution caused by halogenated flame retardance, phosphorous-containing compounds are generally and industrially applied for achieving the flame retardant effect, e.g. phosphorous-containing phenanthrene type compound DOPO and derivatives thereof. Halogen-free polyphenylene oxide resin compositions currently used in electronic circuit boards usually use the addition-type phosphorous-containing flame retardant to achieve the flame retardant requirements, but there are deficiencies in the moisture resistance and chemical resistance. In addition, since the phosphorous-containing phenolic compound is indissoluble in non-polar solvents, such as toluene, the method of redistributing in the solution reported in JP9-235349 and JP3248424 cannot be used for preparing a phosphorous-containing polyphenylene oxide with low molecular weight.